System of distribution.



C. LE G. FORTESCUE.

SYSTEM OF DISTRIBUTION. APPLICATION FILED rams. 19H.

RENEWED MAY l3. 1918.

Patented Nov. 12, 191&

2 SHEETS-SHEET l.

INVENTOR [bar/es [e6 Forfescue WITNESSES:

ATTORNEY 0. LE 6. FOHTESCUE. 'SYSTEM OF DISTRIBUTION.

APPLICATION FILED MAR. 9, 19H. RENEWED MAY l3, I918.

&

um W Y R 1 O. V 6 & 0 A N M F m J S 4 E UNITED STATES PATENT OFFICE.

, CHARLES LE G. FORTESCUE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTBIC & MANUFACTURING COMPANY, A COBPORATION 0F PENNSYL- VANIA.

' SYSTEM OF DISTRIBUTION.

Patented Nov. 12, 1918.

Application filed March 9, 1917, Serial No. 153,606. Renewed May 13, 1918. Serial No. 234,343.

To all whom it may concern:

Be it known that 1, CHARLES LE G. Fon- TESCUE, a subject of the King of Great Britain, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Systems of Distribution, of which the following is a specification.

"'My invention relates to alternating-cur-' rent'distributing systems and it has special relatlon to phase-modifying means whereby polyphase apparatus, such as motors, gen- .erators, rotary converters and the like, may

spective of the load conditions obtaining therein and, at the same time, the powerfactor of the single-phase supply circuit may" be maintained at a substantially constant value. In consequence thereof, polyphase apparatus, such as I have indicated above, may be economically and efiiciently operated from a single-phase power circuit with results comparable to t ose obtained when the polyphase apparatus is operated on polyphase circuits of the usual character.

For a better understanding of. the characteristic features of my invention, reference may be had to the following description and the accompanying drawing in which Figure l is a. diagrammatic view of an electrical distributing system embodying a form of my invention; Fig. 2 is a similar view showin an electrical equivalent of the phasesp ittin device embodied in the system of Fig. 1-; ig. 3 is a vector diagram showlng the relationships between voltage and ourrent vectors. by meansof which the electrical conditions obtaining in my distributing system may be represented; Fig. 4 is a diagrammatic view of a modified form of the system of Fig, 1; Fig. 5 1s a simplified diagram for illustratmg the operation of the phase-splitting device embodied in the system of Fig. 4, and 6 is a vector diagram showing the relations between the electromotive forces obtaining in the phasesplitting device of Fig. 4, under different load conditions.

7 Referring to Fig. 1, a single-phase powersupply circuit, comprising mains 1 and 2,

furnishes power to a phase-modifying device 3 which, in turn, su plies alternating currents to one phase 4 of a polyphase apparatus 5. The apparatus 5 is represented as an induction motor having, in addition to the phase winding 4, a second phase winding 6. The phase winding 6, as will be hereinafter explained, is furnished with power directly from the single-phase supply circuit, while the phase winding 4 is supplied with power through the phasesplitting device 3.

The phase-splitting device 3 comprises adjustable inductive reactance elements 7 and 8 and adjustable condensive reactance elements 9 and 10, all of said elements being connected to a common point 11. The elements 7 and 9 are paired and have their free terminals connected to a secondary transformer winding 12, while the elements 8 and 12 arelikewise paired and have their free terminals connected to a second transformer winding 13. Taps 14 and 15, provided at intermediate points on the windings 12 and 13 respectively, provide means for connecting the phase winding 4 of the polyphase apparatus 5 to the phase-splitting device 3.

A second secondary windinglG, in this instance, comprising two coils that ,together have the same number of conductor turns as are embodied in either the winding 12 or the winding 13, delivers power to the other phase 6 of the polyphase apparatus 5. The secondary windings 12, 13 and 16 of the power transformer are inductively related to a primary winding comprising two 18, through an adjustable lead Thelinember 21 is provided, at its lower end,;-'with a rack 22 which, in turn, engages .a. pinion 23 mounted upon the shaft of a motor 24. As the shaft of the motor 24 rotates, it will be evident that the positions a two-phase induction motor which is de-- signed to operate at a substantially constant slip, under all load conditions. Hence, it follows that the'poWer-factor of the polyphase apparatus will be maintained substantially constant under all load conditions.- Again, assume that the phase'modified voltage derived from the phase-splitting device 3 is equal, in value, to that impressed upon the phase-splitting device by either of the transformer windings 12 and 13. After having determined the slip at which the motor 5 is to constantly operate, the reactive elements 7, 8, 9 and 10 of the phase-splitting device 3 are so adjusted that, at a given load, balanced polyphase conditions will obtain in the two-phase windings 4 and 6 of the motor. After the electrical constants of the elements of the phase-splitting device are once adjusted for a given load on the motor 5, as mentioned above, no further adjusting to is necessary, since the-motor 5 operates at a constant slip or a constant power-factor at all loads.

1 As the loads upon the motor 5 vary, the voltages impressed. upon the two-phase l5 windings thereof'must vary accordingly so that a constant power-factor may obtain in the poly-phase circuits comprising the Windings 4 and 6,-, To "this end, the voltage impressed upon the phase-splitting device is automatically varied, as well as the voltage impressed-upon the secondary winding 16. This ,is accomplished by automatically varying the adjustable leads 19 and 20 on the primary coil-windings 17 and 18 of the power transformer. a

The automatic voltage control is effected by means of 'a diflerential wattmeter relay 25 comprising two superposed wattmeter elements that are mounted upon a common so shaft 26 and severally connected in circuit with the two-phase windings 4 and 6 of the polyphase motor 5. The relay 25 also com-.

rises a. contact-making element 27 that registers upon a scale 28 and is adapted to en- :5 gage either an adjustable contact member 29 or an adjustablecontact member 30, depending upon whether the torque developed by the upper or lowervwattmeter element predominates.- gThe wattmeter 25 is associated with an automatic reversing switch 31 of a well known type of construction. This switch, in turn, controls the direction of rotation ofthe motor 24.. j

The upper wattmeter element is connected in circuit .with the secondary transformer winding 16 and the phase winding 6 of the polyphase device 5. A current coil 32 is connected in series with the secondary transformer winding 16 through a conductor 33 and in series'with the phase winding 6 of the motor 5 through a conductor 34. A

voltage coil 35 of the upper wattmeter element is connected across the phase winding 6 by means of conductors 36 and 37. Similarly, one terminal of a current coil 38 of the lower wattmeter element is connected in V series with a conductor 39 that extends from the tap 15, in this instance, a mid-point tap provided on the secondary transformer winding 13. The other terminal of the cur- 90 rent coil 38 is connected, by means of a conductor 40, the phase winding 4 of the motor 5, a conductor 41 and a conductor 42,,1to the mid-point tap 14 on the transformer secondary winding coil 43 of the lower wattmeter element is connected, by means of conductors '44 and 45, across the phase winding 6. o The two wattmeter elements are so arranged that, when equal amounts of power are furnished to the two-phase windings 4 and 6, the contact-making arm 27 willregister zero. In this instance, balanced polyphase conditions obtain in the/circuits of the polyphase motor 5, since the elements of the phase-splitting device were previously ad justed to attain this end.

If the load upon the polyphase motor 5 is varied, the motor slip will momentarily de part from its normal value which, in turn, will destroy the balanced polyphase conditions in the motor circuits, since the powerfactor of the. polyphase circuits will likewise depart from its normal value. This results in establishing unbalanced polyphase conditions because the phase-splltting device 3 has been previously adjusted to maintain balanced polyphase conditions only when the power-factor in the derived phase of the polyphase circuits is maintained con- 4 stant, By reason of the inequality in the amounts of power supplied to the two phases 4 and 6 of the polyphase motor, the wattmeter relay 25 will effect engagement between the contact making arm 2'2 and either-thecontact member 30 or the contact member 29. The contact member 30 controls the excitation of anelectromagnet 46 of the revers-.

ing switch'31,and the contact member- 29 12. A voltagees I controls the excitation of an electromagnet 47 of the reversing switch 31. When either of the electromagnets 46 and 47 is energized, a magnetizable pivoted arm 48 is advanced in one direction or the other and closes a circuit through the motor 241, either through contact members 19 or through contact members 50 of the reversing switch .31. When the arm 48 engages the contact members 50, a circuit is established through the motor 24; to effect rotation thereof in one direction and, when the arm 48 engages the contact members 49, a circuit is established through the -motor 24 to eifect rotation thereof in the opposite direction.

The diiferential wattmeter relay 25, therefore, selectively controls the direction of rotation of the motor 24 through the reversing switch 31 which is automaticall energized, as will be apparent to all those s 'lled in the art. As the motor 24 is energized, the adjustable taps 19 and on the primary coilwindings 17 and 18 of the transformer willbe varied until balanced polyphase conditions are restored in the polyphase circuits. When balanced polyphase conditions again obtain therein, the differential wattmeter relay will register zero and the motor 24 will be denergized.

51. The derived phase 52, which corresponds.

The phase-splitting device of Fig. 1 may be considered, under certain conditions, as being the electrical equivalent of a tunedbridge, such as is shown in Fig. 2. The tuned bridge of Fig. 2 comprises the condensive elements 9 and 10 andthe inductive elements 7 and 8 which are alternately connected in a closed circuit. A transformer I winding 51 is connected across one diagonal of the tuned bridge and represents either of the windings 12 and 13 of Fig. 1 in that it supplies the exciting voltage to the phasesplitting device. In other words, the bridge of Fig. 2 is excited from a single-phase circuit by means of the transformer winding to the phase winding 4 of the polyphase motor 5, is connected to the other diagonal of the tuned bridge. .The voltage impressed upon the derived phase 52 is equivalent to that impressed upon the mid-point taps 11- and 15 of the transformer windings 12 and 13, respectively, of the transformer of Fig. 1. If the tuned bridge of Fig. 2 should besubstituted for the phase-splitting device 3 of Fig. 1, the electrical conditions obtaining in the system would not be changed. Therefore, a vector diagram representing the ele'ctrical conditions obtaining in the system of Fig. 2 will also represent the conditions obtaining in the system of Fig. 1.

To understand the polyphase conditions established by the .phase-splitting device 3 in the system of Fig. 1, attention is directed to the vector diagram of Fig. 3 in which a vector 0A represents the voltage impressed upon the phase winding 6. In other words, the vector OA represents, in phase and magnitude, the voltages severally impressed upon the windings 12 and 13 which are employed for exciting the phase-splitting device 3. The vector OA is also the equivalent of the vectorial'sum of the vectors OO and OB, representing the voltages impressed uponthe condensive element 9 and the inductive element 7, respectively, or the voltages impressed upon the condensive element 10 and the inductive element 8. This is by reason of the fact that the device 3 effects a one-to-one voltage transformation and the elements 7, 8, 9 and 10 have been so adjusted as to generate the same reactive voltages when-impressed with alternating currents of the same frequency. The voltage obtaining across the taps 14 and 15 of the windings 12 and 13, respectively, or, in other words, the voltage impressed upon the phase winding 4 of the polyphase motor is represented by a vector OD which is the vectorial sum of the vector 00 and a vector -OB. The vectors OA and OD are, therefore, equal to, and disof the vectors OE and OF and is advanced to the extent of the angle I with respect to the voltage vector 0 The vector OG, of course, is the resultant of the urrents supplied to the condensive element 9 and the inductive element 7 Since the vector OO represents the condensive reactance voltage, a vector OH, being a component of the vector OE and leading the vector OO by ninety degrees, represents the current supplied to the condensive element 9. Similarly, a vector OJ, being the other component of the vector OE and lagging ninety degrees behind the vector OB, represents the current supplied to the inductive element 7. The vectors OH and OJ are the two components of the vector OG. The current supplied to the phase-splitting device 3 is represented by the vector OG and the current supplied to the phase winding 6 of the polyphase motor 5 is represented by the vector OF. Therefore, the resultant current obtaining in the single-phase circuit is indicated by a vector OK which is 1n phase coincidence-with the voltage vector GA. The. voltage andthe current in the single-phase recthe single-phase power-supply circuit when balanced polyphase conditions obtain in the polyphase circuits.

j s the loadsupon the polyphase motor 5 are varied, the voltage impressed upon the phase-splitting device 3 and the phase winding 6 will be similarly varied to maintain balanced polyphase conditions in the polyphase circuitsand, at the same time, unity power-factor in the singlephase circuit,

, since the motor 5 is designed to operate at unity power-factor or constant slip under all load conditions. The vector diagram in Fig. 3, therefore, accurately represents the electrical conditions obtaining in the system, irrespective of the value of the balanced polyphase loads in the motor 5.

In Fig. 4, a single-phase supply circuit comprising mains 54, is connected to the terminals of a primary winding of a transformer that comprises two coils 55 and 56.

The coil 56 is connected in series with the coil winding 55 by means of an adjustable lead 57 that engages'exposed taps on the winding56. An adjustable lead 58, adapted to engage exposed taps on the coil winding 55,v is connected to one terminal of the singlephase circuit 54. The adjustable leads 57 and 58 are mounted upon a rack 59 by means of which corresponding taps on the two coil .windings'55 and 56 may be simultaneously engaged. .One secondary winding of the transformer, comprising coils 60 and 61, is

connected through the current coil 32 of the.

differential wattmeter relay 25 to the independent phase winding 4 of the polyphase apparatus 5. ,The derlved phase winding 6 of the polyphase apparatus 5 is connected, through the current coil 38 of the differential'relay 25, to leads 62 and 63 that, in turn, are connected to the contact-making members of a rotatable arm 64 of aphase-modifying device 65.

The rotatable arm 64 is adapted to engage taps 66 and 67 that extend from secondary transformer. windings 68 and 69, respectively. The secondary winding 68 is connected, by means of leads 7 O, to the free terminals of a pair of reactive elements; namely,. an inductive reactance element 71 and a condensive reactance element 72, of

the phase-splitting device 65. The secondphase-splitting device 65. The power-factor meter 77 is of a usual type of construction and, therefore, it is not deemed necessary to explain its construction or operation.

From the foregoing description, it is apparent that the voltages impressed upon the secondary windings 60, 61, 68 and 69 of the transformer may be simultaneously varied by means of moving the rack-59 whereby the number of active turns of the primary coil windings 55 and 56 may be varied in unison.

The reactive elements of the phase-splitting device 65 are adjustable and, likewise, the

position of the rotatable switch element 64 may be varied at will.

The diagram of Fig.5 shows a simplified arrangement of the electrical circuits embodied in the phase-splitting device 65. The leads 62 and 63 are shown as engaging corresponding taps on the twosecondary coils 68 and 69, respectively. It will be under stood that, as the lead 63 is advanced toward wise advanced toward the condensive element 72 in order to occupy a corresponding position.

Referring again to Fig. 4, it may be proved "mathematically that, by varying the positions of the leads 62 and 63 on the secondary transformer windings 68 and 69, respectively, the power factor obtaining in the single-phase supply circuit may be controlled. If it isdesired to maintain unity power factor in the single-phase circuit, the

' leads 62 and 63 will engage mid-point taps on the transformer windings 68 and 69. If it is-desired to maintain either 'a leading or a lagging power factor in the single-phase supply circuit, the leads 62 and 63 will be moved from the mid-point taps to other intermediate taps on the windings, in accordance with the value and character of the the condensive element 75, the lead 62 is likepower factor thatit is desired to maintain in the single-phase supplycircuit.

By means of the vector diagram'of Fig. 6, the distortions in the electromotive forces may be observed that are occasioned by rea.- son of varying the'power factor of the current flowing in the derived phase 6 of the polyphase apparatus. For the purpose of illustration only, it may be assumed that the kilovolt amperes required in the derived phase 6 are constantat all times but that the power factor of the current varies. Let a vector AB represent the derived voltage or that impressed upon the phase windin 6 and a vector I represent the normal lagging impressing voltages of the same value and phase upon said transformer windings, and conductors extending from intermediate'taps of the said transformer windings upon which the phase-modified voltage is innpressed.

3. Avoltage phase-modifying device comprising two inductive and two condensive reactance elements having their electrical constants soadjustedas to generate reactivevoltages of the same value when impressed.

vwith alternating currents of the same frewindings upon which a derived voltage that is displaced at right angles to the voltages obtaining in said transformer windings is impressed. p

4. A voltage phase-modifying device comprising two' inductive and two condensive reactance elements having their electrical constants so adjusted as to establish series I resonance when impressed with alternating currents of the same frequency, the elements being connected to a common point and the condensive elements being severally paired with the inductive elements, two transformer windings being severally connected to the free terminals of the said two, pairs of elements, means for simultaneously impressing, voltages of the same value and phase on said transformer windings, and conductor extending from mid-point taps on said transformer windings upon Which a derived voltage equal to, and displaced atright angles from, the voltages obtaining in saidtransformer windings is impressed.

5. A voltage phase-modifying device comprising two inductive and two condensive reactance elements connected to a common point, the condensive elements being'severally paired with the inductive elements, two transformer windings being severally connected to the free terminals of the said two pairs of elements, means for simultaneously impressing voltages of the same value and phase upon said transformer windings, conductors extending from intermediate taps on the said windingsupon which the phasemodified' voltage is impressed, and automatic means for varying the voltages impressed on said transformer windings,

6. The combination with a power-supply circuit, a load circuit, a phase-modifying means connected to said circuits to enable the phase of the voltage obtaining in the supply circuit to be modified for use in the load circuit, said phase-modifying means mon point; the condensive elements being severally paired with the inductive elements, two transformer windings being severally connected to the free'terminals of said two pairs of elements and simultaneously impressed with equal voltages by the said power-supply circ'i", and conductors comprising the said load circuit extending from intermediate taps on said transformer windings upon which the derived and phasemodified voltage is impressed, of means for maintaining constant power factor in the said power-supply circuit, irrespective of the load obtaining in the load circuit.

7. The combination with a single-phase power-supply circuit, an electrical apparatus having polyphase circuits, phase modifying means connected to said circuits to enable said apparatus to operate on the single-phase circuit, said phase-modifying means comprising two inductive and two condensive reactive elements connected to a common point, the condensive elements being severally paired with the inductive elements, two transformer windings being severally connected to the free terminals of the said two pairs of elements and simultaneously impressed with equal voltages by the single-phase supply circuit and conductors comprising one of said polyphase circuits extending from intermediate taps on said transformer windings. of conductors com prising another of said polyphase circuits extending from said single-phase supply circuit, and means controlled by the conditions obtaining in said polyphase circuits for automatically maintaining unity power factor in the single-phase supply circuit.

8., 'The combination with a single-phase power-supply circuit, an electrical apparatus having polyphase circuits, and means for directly supplying one of the polyphase circuits from the single-phase circuit, of phase-modifying means for enabling the polyphase apparatus to operate on said single-phase circuit, said phase-modifying means comprising two adjustable inductive and two adjustable condensive reactive elements connected to a common point and the condensive elements being severally paired with the inductive elements, two transformer windings being severally connected to the free terminals of the said two pairs of elements and simultaneously impressed with equal voltages by the single-phase supply circuit, taps on said transformer windings, adjustable leads adapted for connection to said taps and comprising one of said polyphase circuits, and means for connecting said adjustable leads-to corresponding taps on the transformer windings whereby a predetermined power factor may be mamtamed the inductive elements and the condensive elements of the device 65, respectively. Since the device 65 is adjusted for a ninety per cent. power factor, the electromotive forces are in balanced polyphase relations and the full-line rectangle indicates the conditions obtaining in this circumstance. Assuming that the power, factor in the derived phase 6 improves to ninety-five per cent. and that the valve of the current remains the same, the current is represented by a vector I and the voltage rectangle, being distorted,

may be represented by the one drawn in dotted. lines. It will be apparent, from inspection, that the two-phase relationship between the impressed electromotive force (PD and the derived electromotive force AB is destroyed and that the voltage vector E representing the voltage impressed on one of the inductive elements, is decreased, while the voltage vector E representing the voltage impressed on one of the condensive elements, is increased.

When the power factor of the current decreases to eighty per cent, as indicated by a vector I, the electromotive force rectangle, being distorted, may be represented by the one drawn in the dot-and-dash lines. The two-phase relationship between the electromotive forces is destroyed again, but the voltages severally impressed upon the inductive elements are considerably increased, as shown by the vectorE while the voltages severally impressed upon the condensive elements are considerably decreased, as shown by a vector E Since the kilovolt amperes in the derived phase 6 are to be maintained constant, irrespective of the power factor of the current,

7 correct two-phase relationship between the voltages may be restored by manually adjusting the constants of the elements 71, 7 2, 74 and 75 of the phase-splitting device 65. In order to maintain unity power factor or any other predetermined power factor in the singlebase circuit, the rotatable switch member 64: is then manually operated until the desired power factor is obtained, as indicated by the power-factor meter 7 7 If it is desired to maintain a power factor whloh results from a lagging current flow in the single-phase circuit, the adjustable leads 62 and 63 should be moved in the direction of the condensive elements, as shown in Fig. 5 and, if it is desired to maintain such power of a leading current,

the adjustable leads 62 and 63 should be 56 moved to points adjacent the inductive elements 71 and 74 of the phase-modifying relations may be maintained in the polyphase circuits and the desired power factor in the single-phase circuit by making the following adjustments: The constants of the reactive elements comprising the phasemodifying device are to be adjusted simultaneously with the voltages impressed upon the secondary windings of the transformer supplying power to the polyphase apparatus 5. These adjustments are to be made until the differential wattmeter relay 25 registers zero, thereby indicating that balanced polyphase conditions obtain in the polyphase circuits. Under this circumstance, the currents obtaining in the several polyphase circuits are equal in value and lag or lead with reference to their respective electromotive forces by the same amount. Then the position of the rotatable arm 64 is to be varied until the power-factor instrument 77 registers the desired value, thereby indicating that the power factor of the singlephase circuit is restored to its predetermined value.

The above explanation of the operation of the system shown in Fig. 4 assumes that the phase-modifying device 65 possesses a oneto-one voltage transformation, that is, the voltages severally impressed upon the device by the windings 68 and 69 are equal in value to the voltage impressed upon the derived phase of the polyphase circuits.

While I have shown and described, in detail, one embodiment of my invention, it will be understoodthat many modifications may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. A phase-modifying device comprising inductive and condensive reactance elements connected to a common point, the condensive elements being severally paired with the inductive elements, a winding connected to the free terminals of each pair of said elements, means for simultaneously impressing voltages of the same value and phase on said windings, and conductors extending from intermediate taps on said windings upon which the phase-modified and derived voltage i impressed.

.2. A voltage phase-modifying device com prising two inductive and two condensive reactance elements connected to a common point, the condensive elements being severally paired with the inductive elements, two transformer windings being severally connected to the free terminals of the said two rec inthe single-phase circuit, irrespective of the load conditions obtaining in the poly- ,phase circuits.

- ductive and two adjustable condensive re- ,ary transformer win active elements connected to a common point and the condensive elements being severally paired with the inductive elements, a transformer having its primary winding connected to the single-phase circuit and two secondary windings that are severally connected to the free terminals of said two pairs of elements and simultaneously impressed with equal volta ges, taps on said transformer windings, adjustable leads adapted forconnection to said taps and comprising one of said polyphase circuits, and means for connecting said adjustable leads to correspondin taps on said-secondings whereby a predetermined power factor may be constantly maintained in the single-phase circuit, irrespective of the load conditions in the polyphase circuits.-

10. The combination with a power-supply-circuit, an electrical apparatus having polyphase circuits, and means for directlysupplying at least one of said polyphase circuits'from said single-phase circuit, of phase-modifying means connected to at least one of said polyphase circuits to enable the polyphase apparatus to operate on the single-phase c1rcuit,. said phase-modifyingmeans comprisingtwo adsingle-phase justable inductive and two adjustable condensive reactive elements connected to a common point and the condensive elements being severally paired with the inductive elements, a transformer having its primary winding connected to the single-phase circuit and two secondary windings that are severally connected to the free terminals of said two pairs of elements and simultaneously impressed with equal voltages, taps on said transformer windings, adjustable leads adapted for connection to said taps and comprising one of said polyphase circuits, means for connecting said adjustable leads to corresponding taps on said secondary transformer windings whereby a predetermined power factor may be constantly maintained in a single-phase-circuit irrespec tive of the load condition in the polyphase circuits, and means for varying the voltage impressed on the said secondary transformer windings in accordance with the polyphase loads obtaining in the polyphase circuits.

11. A. phase-modifying device comprising two inductive and two condensive reactance elements connected to a common point, the condensive elements being severally I paired with the inductive elements, a transformer having a primary winding and two similar secondary windings that are severally connected to the free terminals of the said two pairs of reactance elements, taps on said secondary windings, adjustable leads across which the phase-modified voltage is impressed, and means for connecting said adjustable leads to corresponding taps on said secondary transformer windings.

In testimony whereof, I have hereunto subscribed my name this 8th day of March,

CHARLES LE G. FORTES TE. 

